Method for coating steel with white metal



United States Patent O 3,406,445 METHOD FOR COATING STEEL WITH WHITEMETAL Giinter Kiipke, Heilbronn (Neckar), and Friedrich Wilhelm Rabenau,Neckarsulm, Wurttemberg, Germany, assignors to Karl Schmidt G.m.b.H., Neckarsulm, Wurttemberg, Germany, a corporation of Germany No Drawing.Filed Sept. 20, 1965, Ser. No. 488,794 Claims priority, applicationGermany, Oct. 17, 1964, Sch 35,977 8 Claims. (Cl. 29492) ABSTRACT OF THEDISCLOSURE Coating white metal onto a tinned steel sheet by heating thetinned steel sheet to a temperature higher than the melting point of thewhite metal, applying solid white metal at ambient temperature to theheated tinned steel sheet and pressing the two together between niprollers.

This invention relates to a method for applying coatings comprising aPb-Sb-Sn-As alloy commonly referred to as white metal; morespecifically, this invention relates to a method for coating steel withwhite metal.

The prior art teaches that while metal may be applied to steel which istinned in a hot-tinning process, after which molten white metal is thenapplied to the hot-tinned steel. The white metal is then reduced to thedesired thickness by scraping and milling. These prior art methods ofcoating are relatively complicated and expensive.

It is therefore an object of the present invention to overcome these andother difiiculties encountered in the art and to obtain a new method forcoating with white metal that is quicker and less expensive than theprior art process. It is a further object of this invention to provide amethod for coating with white metal in which smooth coatings of adesired thickness may be obtained initially without further machining. Afurther object of this invention is to provide a method for coatingwhite metal at fine tolerances of coating thickness and smoothness. Anadditional object is to apply such coatings to steel which has beentinned by either a hot-tinning or galvanic process. An additional objectof this invention is to provide a method for applying solid white metalcoatings to tinned surfaces, thereby obviating the difficultiesencountered in the prior art with molten white-metal coatings. It isanother object of this invention to provide as an article of manufacturea precision white metal bearing or anti-friction device.

These and other objects have been obtained by the present inventionwhich comprises coating steel with white metal in which commerciallyavailable tinned continuous sheet steel is heated preferably byinduction to 320 to 380 C. under a protective gas, and in which whitemetal in the form of cut or continuous sheets is pressed onto the steelthrough a roller gap or other suitable press means at room temperature,whereupon the white metal is pressed or plated onto the steel. In thisprocedure the steel remains practically undeformed, while the whitemetal is subjected to a deformation of 20 to 50 percent or 60 percent.The adherence of the plating produced according to the invention isperfect. Although commercially available tinned sheet steel isapproximately 25 percent more costly than untinned steel, an overallcomparison of the present invention shows that it is more economicalthan the prior art methods and articles produced thereby.

The white metal used in the method of the present invention is known inthe art and generally comprises an alloy of lead, antimony, tin andarsenic in ratios which are also Well known in the art.

During the pressing operation of the present invention, the white metalis caused to flow or deform. Deformation and flow are synonymous in thisrespect and either term is used to indicate that in general thethickness of the white metal is reduced under such pressing conditions.The degree of pressure needed to obtain the bond between the white metaland the tinned steel is directly related to the degree of deformation ofthe white metal obtained when practicing the method of the presentinvention.

The adhesive bond is obtained through the intermediate tinning, andalthough the present invention is directed primarily to a method forobtaining a white metal coating on steel, any tinned surface may becoated in such a manner. Additionally, a non-continuous process may beutilized in place of the nip-roll pressing means used for coating whilemetal according to the present invention. In this respect, any type ofmeans may be used for applying pressure to the white metal and thesurface to which it is applied.

It is one of the essential features of the present invention that Whitemetal may be applied as a coating in substantially a solid state. Theprior art difficulties encountered in applying molten white metalcoatings are thereby obviated. The non-molten or substantially solidwhite metal applied according to the method of this invention ispreferably coated in the formof continuous or discontinuous sheets,however, the coating may also be applied as a powder according to powdermetallurgy techniques which are well known in the art.

The tinned surface to which the white metal coating is applied must beheated to approximately 320 C. to 380 C., and the white metal applied attemperatures lower than the tinned surface, preferably at ambient orroom temperature, i.e., 20 C. The temperature of the white metal must below enough so that the white metal when applied is non-molten or solid.The substrate to which the white metal is applied must be of sufficientstrength so that at the elevated temperatures at which the coating isapplied, the substrate Will have sufiicient structural integrity so asto permit 20 to 50 percent, or 60 percent deformation of the whitemetal. In the preferred embodiments of the present invention, the steelsubstrate exemplifies these properties, whereby, after heating to320-380 C. and application of the white metal coating, the steelsubstrate substantially maintains it thickness and other dimensions,Whereas the white metal coating is deformed.

The shielding gas employed according to the method of the presentinvention can be any gas known in the art suitable for this purpose,such as the -so-called noble gases or reducing gases such as carbonmonoxide or hydrogen or nitrogen or any gas that will prevent oxidationof the metal during the heating and pressing operations withoutadversely combining with the metal.

The following non-limiting examples are included as certain preferredembodiments of the invention and are not to be construed as narrowingthe scope of the invention.

Example I A low-carbon sheet steel (approximately St4 supplied in coilform is galvanically tinned on one side in the customary manner with acoating of 5 to 8 mu of tin. A white metal composed of 13.5 percent Sb,1.5 percent Sn, 1 percent As, and the balance Pb is cast into rollingingots of 20 mm. thickness, rolled down to 1 mm. at approximately 180C., and roughened on one side with wire brushes. The tinned sheet steelis then continuously heated by induction at medium frequency to 280 C.,and fed through an induction coil directly into the nip of a rollingmill under a shielding gas.

The sheet, roughened on one side, is likewise fed to the rolling millnip, and squeezed in the roller gap onto the hot, tinned steel sheet,the steel undergoing no deformation and the white metal of 1 mm.thickness being reduced to 0.5 mm. thickness. When the white metal hasbeen sweated onto the tinned surface of the steel, it can be furtherformed into rolled bushings or split bushings for friction bearings. Thesurface of the white metal and of the steel remains smooth, having aroughness of less than 1 mu, so that no further machining is needed.

Example 11 The procedure of Example I is repeated using a commerciallyavailable hot, tinned steel with a tin coating of 4 to 12 mu which isinductively heated to 300 C. under a shielding gas. Just ahead of theroller gap, a white metal alloy of the Pb-Sb-Sn-As type, rolled fromeast ingots into sheet form, is cold-rolled'onto the steel. The finalcoating thickness of the white metal in this example is 0.2 mm. Thewhite-metal sheet was rolled to a thickness of 0.35 mm. from the ingot,before application to the tinned steel sheet. The white metal adhered tothe steel sheet is used as a bearing.

Example 111 A white-metal-coated steel strip is prepared for socalledmicro-bearings, in which the white metal thickness amounts to only 50 to70 mu. In this example, a white metal sheet, 0.1 mm. thick, is rolledonto galvanically or hot tinned, heated steel strip. The laminating iseffected and takes place in the same manner as described in Example I,although the easily torn, thin foil had to be fed to the roller gap inthe cold state by means of a foil dispenser, according to methods knownin the art. In this case again, any subsequent machining of the whitemetal or of the steel surface is unnecessary, and is even impossible inthe latter case.

Thus, there has been described a novel method and article ofmanufacture, whereby a solid white-metal coating is applied to a tinnedsubstrate, whereby smooth coatings of a desired thickness are obtainedinitially without further machining, the coatings being held to finetolerances of coating thickness and smoothness. The coatings are formedby pressing the white metal onto a hot, tinned substrate in such amanner so that the white metal under-v goes between 20 to 50, or 60percent deformation. By the application of white-metal coatings to atinned steel substrate, according to the method of the presentinvention, an article of manufacture is obtained comprising a precisionwhite metal bearing or anti-friction device.

Although the invention has been described with reference to certainpreferred embodiments, it is not intended that the invention be limitedthereby, and certain modifications of thenovel method and article ofmanufacture are intended to be included within the broad scope of thefo'llowing claims.

1. A method for plating white metalonto steelj'comprising heating atinned steel surface to'a' temperature from 280 C. to 380 'C., pressingasolid'white metal strip at ambient temperature onto said tinned steel,leading said white metal and said steel simultaneously through niprollers and pressing said white metal into a plating relationship withsaid steel in said nip rollers at pressures sufficient to-plate saidWhite metal ontosaid steel and to exclusively deform saidwhite metal,with said steel remaining substantially undeformed, whereby a whitemetal coating is obtained having a surface smoothness of less than onemicron.

2. Method as claimed in claim 1 wherein said steel surface is heated toa temperature of about 320 to 380 C.

3. The method of claim 2 where said heating is conducted inductively.

4. The method of claim 2, where said pressing is conducted under ashielding gas.

5. The method of claim 2, where said white metal comprises an alloyfofPb, Sb, Sn, and As.

6. The method of claim 5, where said alloy comprises 13.5 percent Sb,1.5 percent Sn, 1 percent As and the balance Pb. z

7. The method of claim 2 where said white metal is reduced by an amountcomprising 20 percent to percent during said pressing.

8. The method of claim 2, where said white metal before plating variesfrom 0.35 to 1.0 mm. in thickness.

References Cited V UNITED STATES PATENTS 1,956,464

JOHN F. CAMPBELL, Primary Examiner.

D. C. REILEY, Assistant Examiner.

